In a PMA standard wireless charging device, its energy transmitting terminal (TX) usually sends a FSK signal at the beginning of the whole system operation, and at this time, an operating frequency of a TX signal is from 215 KHz to 220 KHz in the PMA-3 system, from 142 KHz to 158 KHz in the PMA-4 and PMA-5 systems, from 109 KHz to 121 KHz in the PMA-6 system, from 140 KHz to 158 KHz in the PMA-7 system, and from 220 KHz to 226 KHz in the PMA-8 system. Fmod is Fop+Mdepth, and a value of a cycle difference Top-Tmod between a carrier frequency Fop and a modulation frequency Fmod can be calculated to be from 96 ns to 770 ns. A piece of data is sent every 500 us, and data 1 and data 0 are sent in ways as shown in FIG. 1.
In the PMA (Power Matters Alliance) standard wireless charging device, a communication signal sent from an energy transmitting terminal to an energy receiving terminal is transmitted by means of frequency conversion, and the problem lies in that in the PMA-3, PMA-4, PMA-5, PMA-6, PMA-7, and PMA-8 standard communication protocols, a communication carrier frequency Fop of a signal sent by an energy transmitting terminal (TX) is not unique (109 KHz≤Fop≤226 KHz), and a frequency difference between Fop and Fmod is not fixed but only has a certain frequency difference range, i.e., having a modulation depth Mdepth (5 to 10 KHz), and thus the same power receiving system may need to simultaneously support the above six types of energy transmitting terminals (TX) based on different PMA protocols.
At the same time, since a signal received by an energy receiving terminal in a wireless charging system is an inductively coupled signal, the received signal is not a single frequency sinusoidal signal, and instead, it may be doped with a large amount of high frequency noise. The traditional 2 FSK demodulation methods are mainly three ways: coherent demodulation, filtering non-coherent demodulation and quadrature multiplication non-coherent demodulation.
Due to the limitation of the PMA standard communication protocol, a difference value between a carrier frequency Fop and a modulation frequency Fmod is fixed within a certain range, such that the higher the frequency of Fop is, the smaller the cycle difference between Fop and Fmod is. If demodulation is done using traditional methods, the entire system requires very high precision to distinguish different frequencies, which will greatly increases the expenditure of the entire circuit no matter an analog manner or a digital manner is achieved. At the same time, in different PMA transmission systems, the carrier frequency Fop in the communication phase is not fixed to a certain value between 110 KHz and 205 KHz (the PMA protocol only provides a range), which may greatly increase the expenditure of the entire demodulation system.